Now that the toolchain is installed, you can start using it. From the
command line, you can compile a project using gprbuild. For
example:

gprbuild -P project.gpr

You can find the binary built with the command above in the obj
directory. You can the run it in the same way as you would do with any
other executable on your platform. For example:

obj/main

A handy command-line option for gprbuild you might want to use
is -p, which automatically creates directories such as obj if they
aren't in the directory tree:

gprbuild -p -P project.gpr

Ada source-code are stored in .ads and .adb files. To view the
content of these files, you can use the GNAT Programming Studio
(GPS). To open GPS, double-click on the .gpr
project file or invoke GPS on the command line:

gps -P project.gpr

To compile your project using GPS, use the top-level menu to
invoke Build → Project → main.adb (or press the
keyboard shortcut F4). To run the main program, click on
Build → Run → main (or press the keyboard shortcut
Shift+F2).